For pollutant minimization in catalytic aftertreatment of exhaust gases with the aid of a closed-loop, three-way catalytic converter, it is known in the art that the air-fuel mixture should have a specific mass ratio. This ratio is indicated by the so-called excess-air factor “lambda”, and can be detected by a lambda sensor located in the exhaust pipe.
In known methods, the values measured by the lambda sensor are fed to a control loop which controls the injection quantities of the individual cylinders as a function of the lambda value during operation of the internal combustion engine.
However, in the case of a single lambda sensor located in the exhaust pipe, this closed-loop control is based only on the lambda value that is averaged over the individual cylinders.
Mixture differences in the individual cylinders which arise in spite of equal injection quantities or equal setpoint values of a control unit for the injection quantities, due to component tolerances and aging effects, cannot be predetermined or taken into account with respect to the calculation of the cylinder-specific injection quantity.
Some methods provide for a temporal assignment of the exhaust gases flowing through the exhaust pipe, and the lambda values thereof, to the individual cylinders. In this manner, the injection quantity can, in principle, be controlled individually for each cylinder by a single lambda sensor, but the measuring accuracy is impaired by mixing effects and turbulences of immediately successive exhaust quantities of different cylinders in the exhaust pipe.
Design approaches in which each cylinder is assigned a lambda sensor are technically very complex.
It is therefore an object of the present invention to provide a method for cylinder-specific adjustment of the injection quantity in internal combustion engines with one lambda sensor located in the exhaust pipe.